99 Cobra IRS rearend questions:

Discussion in 'Drivetrain' started by chuddleston2003, Apr 22, 2014.

  1. chuddleston2003

    chuddleston2003 Member

    Messages:
    135
    Likes Received:
    4
    Joined:
    Jul 1, 2008
    Hey everyone I am going to be putting in a T56 tranny and I am going to be upgrading the rearend for the power I will be putting the ground. I will be hopefully putting 600-700 rwhp and I am going to upgrade the axles to 31 spline and was wondering if I need to upgrade the differential also with a 31 spline since I think the T56 tranny has the 31 spline shaft. Any help would be greatly appreciated.
     
  2. RichV

    RichV Well-Known Member

    Messages:
    4,227
    Likes Received:
    247
    Joined:
    May 6, 2012
    Location:
    CO
    The tranny has nothing to do with the dif splines. If you get 31 spline axles, you need a 31 spline diff.
     
  3. Win

    Win Legend

    Messages:
    9,514
    Likes Received:
    8
    Joined:
    Nov 20, 2006
    Location:
    Kennesaw, Ga

    Dont get a 99 they have full 28 spline. Get a 03/04 they have the 31 spline and the torque brace already on there. the cost of doing all the upgrades you would be better off starting with a 03/04. Then no upgrades are needed besides bushings. Unless you plan on going crazy with the FTBR kits.

    You will have to upgrade the diff to accept the new 31 spline axles. A lot of guys that have 01's will upgrade to the 03/04 axles bc they will handle more power and be gotten for cheap.
     
  4. chuddleston2003

    chuddleston2003 Member

    Messages:
    135
    Likes Received:
    4
    Joined:
    Jul 1, 2008
    I already have the 99 cobra I am going to be rebuilding it from the ground up pretty much like Deeplist is doing with the white cobra he bought.
     
  5. Win

    Win Legend

    Messages:
    9,514
    Likes Received:
    8
    Joined:
    Nov 20, 2006
    Location:
    Kennesaw, Ga

    Okie dokie

    well you need a new diff to upgrade to 31 spline. THe problem with the 99's is he cv axles taper down and that's there weak point along with the 28 spline. The 03/04 are a constant diameter.
     
  6. chuddleston2003

    chuddleston2003 Member

    Messages:
    135
    Likes Received:
    4
    Joined:
    Jul 1, 2008
    That is why I am going to upgrade I am hoping to be making around 6-700 rwhp.
     
  7. Win

    Win Legend

    Messages:
    9,514
    Likes Received:
    8
    Joined:
    Nov 20, 2006
    Location:
    Kennesaw, Ga
    FTBR I've always been a huge fan of everything.